For example, in the case of an air hose, a filler hose or the like, it is recently examined and actually practiced that a resin hose is used instead of a rubber hose. The resin hose has the following advantages. The resin hose is capable of decreasing weight of the hose in comparison with the rubber hose since the specific gravity of resin is small. The resin hose is capable of forming an integral-mold article comprising a soft portion and a hard portion. The resin hose is capable of selecting a design for a hose-configuration and so on optionally.
In the case of the resin hose, a hard resin material is used as a portion requiring hardness, a soft resin material is used as a portion requiring softness, and it can be accomplished that the hard hose-portion and the soft hose-portion are molded integrally by using two kinds of resin-material.
On the other hand, in the case of the rubber hose, it is difficult to accomplish that the hard hose-portion and the soft hose-portion are molded integrally. In the case of the rubber hose, in general, a metal pipe is used as a portion requiring hardness, a rubber hose is used as a portion requiring flexibility, and thereby both are constructed together.
In the case of the resin hose, as understood from the above-described, the number of parts can be decreased and a production cost can be decreased since the integral-mold hose is formed by molding the soft portion and hard portion together.
In the case of the resin hose, to select the design for a hose-configuration and so on optionally, which means that the hose is sufficiently endurable against deformation when a negative pressure is applied on the hose. In the case of the rubber hose, for example, providing that the hose is in a flat-shape in cross-section, the flat-shape portion is likely to deform. Accordingly, the selection of the design for hose-configuration and so on is restricted in comparison with the resin hose.
By the way, in the case of the resin hose, a blow molding method is preferably used to form the hose. In the blow molding method, a tubular or a bladder-like parison is swelled by blowing an air so that the parison is closely adhered to an inner surface of the mold-die. As a result, the parison is formed in the predetermined shape. Thus, the outer surface of the mold-hose is accurately formed in the predetermined shape by the mold-die, but the inner surface of the mold-hose is formed under the free condition. Therefore, the inner surface of the mold-hose shows bad characteristics in its shape and dimensional accuracy.
In the hose, a mating member is inserted into the inside of the hose-end portion constituting a connecting portion, and both are connected together. In this arrangement, it is required that sealing capacity can be ensured between the mating member and the connecting portion. Providing that the mold-hose shows bad characteristics in its shape and dimensional accuracy, namely, that defects such as an unevenness thickness, an unevenness dimension, a biased thickness, and a ruggedness are generated, the sealing capacity can't be ensured satisfactorily between the mating member and the connecting portion.
Then, in the case of the aforementioned resin hose formed by the blow molding method, the inner surface is polished for finishing-treatment so that the inner surface of the hose is formed in the predetermined accurate shape and dimension.
In the case where the above-mentioned polishing is performed, not only hose forming steps become complicated, but also polishing powders remain at and around the polishing portion. Therefore, a cleaning step for removing the polishing powders is needed, and the hose forming steps become more and more complicated. As a result, the production cost of the hose is increased.
In order to the aforementioned problems, as illustrated in FIG. 9, the present inventors have developed a process invention, in which a hose body 100 is formed by blow-molding thermoplastic resin, and the hose body 100 is disposed in a mold-die 102, next a tubular connecting portion 104 (an end portion of the hose in an axial direction) for connecting a mating member is formed by injection-molding. This invention has been filed as a patent application (Japanese Patent Application No.3-39145).
In this process invention of the patent application; since the inner peripheral surface of the connecting portion 104 can be formed in the predetermined shape and the predetermined dimension, the polishing of the inner peripheral of the connecting portion 104 isn't needed as distinct from the conventional hose. In this process invention, therefore, not only the polishing step is omissible, but also the cleaning step for removing the polishing powders is unnecessary, thereby the whole number of steps of the process can be reduced and the production cost can be decreased.
Further, in this process invention of the patent application, the inner peripheral surface of the connecting portion 104 can be formed more accurately in comparison with that of the connecting portion polished. Accordingly, for instance, when the mating member such as a metal pipe is inserted into the connecting portion of the hose, the reliability of the sealing capacity between the mating member and the hose is improved.
Furthermore, this process invention of the patent application is advantageous in achieving that the hose body can be made of hard resin and the connecting portion can be made of soft resin.
For example, in the case of the air duct hose for an automobile, since the negative pressure is applied to the hose during use of the hose, providing that the hose body is made of the soft material, the cross-section of the hose body is deformed, and the section thereof is reduced. Therefore, the pressure-loss of an air passing through the hose is increased, the amount of the passing-air is decreased, and thereby the incomplete combustion of the engine may be caused. Providing that the whole hose is made of a hard material with the object of preventing these problems, the sealing capacity between the hose and the mating member is decreased during connecting.
When the hose is made of the hard material and the connecting portion is made of the soft material in view of the above-mentioned process invention of the patent application, not only the hose can possess mechanical strength such as negative-pressure resistance, but also the sealing capacity between the connecting portion and the mating member can be improved. Of course, when a bellows portion is formed in the hose body, or when the bellows is made of soft resin, the hose can become more flexible.
By the way, in the case where the mating member is inserted into the hose, as shown in FIG. 10(A), a concaved portion 106, whose inner diameter is large, is formed at an end portion of the connecting portion 104, and the mating member is inserted into the concaved portion 106 for fixation. In this arrangement, however, when oscillation or bending force is applied to the hose, as understood from FIG. 10(B), a large strain or a large stress generates partially in the connecting portion 104 made of the soft material.
Therefore, cracks generate or progress in the connecting portion 104, the hose may come to be broken off finally.
The present invention has been developed in view of the solving of aforementioned problems.